Magnetic head for rotary head drum

ABSTRACT

A magnetic head for a rotary head drum is disclosed which can suppress abrasion thereof while a sufficient contact thereof with a magnetic tape is secured. An upper side tape sliding surface and a lower side tape sliding surface are formed on a tape sliding surface at an end of a head chip on the opposite upper and lower sides of a central tape sliding surface, which has a magnetic gap thereon, with a pair of upper and lower grooves left therebetween. The upper side tape sliding surface which is brought into contact with a magnetic tape earlier than the central tape sliding surface is formed with an increased thickness while the lower side tape sliding surface which is brought into contact with the magnetic tape later than the central tape sliding surface is formed with a decreased thickness. Also a magnetic head for a rotary head drum is disclosed wherein a pair of upper and lower grooves are inclined with respect to the direction of rotation of the head chip to prevent a foreign substance such as a magnetic particle transferred from the magnetic tape to the tape sliding surface of the head chip from sticking to and being accumulated in the magnetic gap of the head chip.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a rotating magnetic head suitable foruse with a rotary head drum of a high density magnetic recording and/orreproduction apparatus of the helical scanning type such as a video taperecorder (VTR) or a tape streamer, and more particularly to a technicalfield which relates to the shape of a head chip for a magnetic head.

[0002] Conventionally, in a plurality of rotating magnetic headsincorporated in a rotary head drum of a VTR, a tape stream or the like,a magnetic gap in the form of a slit having a width equal to the widthof a signal recording track is formed at a substantially center of atape sliding surface, which contacts with a magnetic tape, at an end ofa head chip formed from a magnetic core.

[0003] The head chip helically scans the magnetic tape at a high speedto record or reproduce (write or read) a signal (data) onto or from themagnetic tape through magnetism conversion at the gap thereof.

[0004]FIGS. 12 and 13 show a rotary head drum 1 of a high densityrecording and reproduction apparatus of the helical scanning type of aconventional VTR, tape streamer or like apparatus. Referring to FIGS. 12and 13, the rotary head drum 1 shown includes a plurality of rotatingmagnetic heads 6 including a plurality of recording heads 4 and aplurality of reproduction heads 5 mounted radially by means of screws 7on and along an outer circumference of a lower end edge of a rotary drum3 which is rotated above a fixed drum 2.

[0005] Each of the rotating magnetic heads 6 has a head chip 11 securelymounted at a radially outer end thereof. When the rotary drum 3 isrotated at a high speed in a direction indicated by an arrow mark bwhile a magnetic tape 21 is helically wrapped on an outer periphery ofthe rotary head drum 1 along a tape lead 8, which is a stepped portionformed helically on an outer circumference of the fixed drum 2, and isfed at a constant speed in a direction indicated by an arrow mark a, themagnetic tape 21 is helically scanned by the head chips 11 of therotating magnetic heads 6 so that helical, high density recording orreproduction of signals (data) onto or from the magnetic tape 21 isperformed.

[0006] Referring now to FIGS. 14, 15A and 15B, each of the head chips 11has a tape sliding surface 12 and a magnetic gap 13 formed at a radiallyouter end thereof. The tape sliding surface 12 is formed in asubstantially arcuate shape along two directions including the rotationdirection b and a direction perpendicular to the rotation direction b,and the magnetic gap 13 is formed at a substantially central portion ofthe tape sliding surface 12 in the rotation direction b. A pair of upperand lower grooves 14 and 15 for permitting escapement of airtherethrough are formed in parallel to the direction of the arrow mark bon the opposite upper and lower sides of the magnetic gap 13. The headchip 11 thus records (writes) or reproduces (reads) a signal at a highdensity onto or from a signal recording surface 21 a of the magnetictape 21 through electromagnetism conversion at the magnetic gap 13. Inparticular, upon signal recording, an electric signal is converted intomagnetic fluxes, but upon reproduction, such a magnetic signal isconverted into an electric signal.

[0007] More particularly, referring to FIG. 16, upon signal recording,the signal recording surface 21 a of the magnetic tape 21 which is fedat a constant speed in a direction of an arrow mark a is helicallyscanned at a high speed in a direction of an arrow mark b from a loweredge 21 b toward an upper edge 21 c of the magnetic tape 21 by the headchips 11 of the plurality of recording heads 4 to successively recordbelt-like signal tracks (belt-like signal recording patterns) TR1, TR2,TR3, TR4, . . . TRn at a fixed track pitch P onto the signal recordingsurface 21 a of the magnetic tape 21 by means of the magnetic gaps 13 ofthe head chips 11. On the other hand, upon signal reproduction, thesignal tracks TR1, TR2, TR3, TR4, . . . , TRn of the magnetic tape 21are helically scanned in the direction of the arrow mark b successivelyby the head chips 11 of the plurality of reproduction heads 5 similarlyas upon recording to successively reproduce the signal tracks TR1, TR2,TR3, TR4, . . . , TRn.

[0008] In order to achieve higher density recording for allowingrecording and reproduction for a longer period of time while decreasingthe consumed amount of magnetic tapes in the magnet recording andreproduction apparatus of the helical scanning type which uses amagnetic tape as described above, two countermeasures are availableincluding a countermeasure of decreasing the track width of the signaltracks TR to be recorded onto the magnetic tape 21 and anothercountermeasure of decreasing the wavelength of a signal to be recorded.However, whichever one of the countermeasures is adopted, a drop of thehead output cannot be avoided.

[0009] On the other hand, it seems a possible idea to decrease the depthof the magnetic gap 13 of the rotating magnetic head 6 to increase thehead output. However, if the depth of the magnetic gap 13 is decreased,then even if the abrasion amount of the head per unit time is equal, themagnetic gap 13 opens in shorter time. Consequently, replacement of therotating magnetic head 6 after a shorter interval of time is required,and a rise of the maintenance cost cannot be avoided.

[0010] In order to reduce the abrasion of the head, it seems a possibleidea to increase the head contacting width over which the tape slidingsurface 12 of each of the head chips 11 of the rotating magnetic head 6contacts with the magnetic tape 21 to decrease the contacting pressureof the magnetic tape 21 with the tape sliding surface 12. It is to benoted that increase of the head contacting width decreases the abrasionof the magnetic gap 13.

[0011] Incidentally, the most significant factor of the head abrasion isa great number of very small magnetic particles of approximately severaltens nm and so forth which naturally stick to the signal recordingsurface 21 a of the magnetic tape 21 in a manufacturing process of themagnetic tape 21, and when the head chip 11 of the rotating magnetichead 6 helically scans the signal recording surface 21 a of the magnetictape 21, the tape sliding surface 12 of the head chip 11 is abraded bygrinding force of the very small magnetic particles and so forth.

[0012] Particularly, when a fresh portion of the signal recordingsurface 21 a of a new magnetic tape 21 on which no signal track TR iswritten as yet is helically scanned for the first time by a head chip11, the head abrasion amount by the grinding force of the very smallmagnetic particles and so forth is naturally greater than that when anold portion of the signal recording surface 21 a on which signal tracksTR are written already is helically scanned.

[0013] The reason why the head abrasion amount can be reduced byincreasing the head contacting width of a head chip 11 is described withreference to FIGS. 15A, 15B and 17.

[0014]FIG. 15A shows a head chip 11S which is a conventional popularhead chip wherein the head contacting width W1 of the tape slidingsurface 12 is small while FIG. 15B shows a head chip 11L wherein thehead contacting width W2 of the tape sliding surface 12 is increaseduniformly in upward and downward directions.

[0015]FIG. 17A illustrates a manner wherein the “head 1”, “head 2”,“head 3” and “head 4” each including the head chip 11S having the tapesliding surface 12 of the small head contacting width W1 successivelyhelically scan the signal recording surface 21 a of the magnetic tape21, which is fed at a constant speed in the direction of the arrow marka, in order at a high speed in the direction of the arrow mark b at afixed track pitch P.

[0016] Meanwhile, FIG. 17B illustrates a manner wherein the “head 1”,“head-2”, “head 3” and “head 4” each including the head chip 11L havingthe tape sliding surface 12 of the great head contacting width W2successively helically scan the signal recording surface 21 a of themagnetic tape 21, which is fed at a constant speed in the direction ofthe arrow mark a, in order at a high speed in the direction of the arrowmark b at a fixed track pitch P.

[0017] Since, in order to increase the recording density, it isnecessary to decrease the width W3 of the magnetic gaps 13 of the headchips 11S and 11L which corresponds to the track width of the signaltracks TR to be recorded onto the magnetic tape 21, the head contactingwidth W1 or W2 is inevitably greater than the width W3 of the magneticgap 13.

[0018] Accordingly, whichever one of the head chips 11S and 11L is used,when the tape sliding surfaces 12 of the “head 1”, “head 2”, “head 3”and “head 4” successively helically run (slidably move) on the signalrecording surface 21 a of the magnetic tape 21 in order at a fixed trackpitch P, a lower side portion of a run portion (running locus) of thesignal recording surface 21 a along which the tape sliding surface 12 ofeach head runs with the head contacting width W1 or W2 overlaps with anupper side portion of a run portion (running locus) of the signalrecording surface 21 a along which the tape sliding surface 12 of apreceding head runs with the head contacting width W1 or W2.

[0019] In FIG. 17A, an overlap portion of a run portion by a succeedinghead with a run portion by a preceding head among the “head 1”, “head2”, “head 3” and “head 4” which each includes the head chip 11S of thesmall head contacting width W1 is indicated as “twice run portion”.

[0020] In particular, in the case described above, a lower side portionof a run portion by a succeeding head overlaps, only once at a portionindicated as “twice run portion”, with an upper side portion of a runportion of a preceding head and besides over a comparatively smalloverlap width. Accordingly, in each “once run portion” which does notoverlap with another run portion and has a comparatively great width, ahead runs on a normally new portion of the signal recording surface 21 aof the magnetic tape 21 on which no preceding head has run (slidablymoved). Also the magnetic gap 13 of a succeeding head always runs on anew portion of the signal recording surface 21 a of the magnetic tape 21on which no preceding head has run (slidably moved).

[0021] Meanwhile, in FIG. 17B, overlap portions of a run portion bysucceeding heads with a run portion by a preceding head among the “head1”, “head 2”, “head 3” and “head 4” which each includes the head chip11L of the great head contacting width W2 are indicated as “twice runportion” and “three-time run portion”.

[0022] In particular, in the case just described, a lower side portionof a run portion by a succeeding head overlaps, twice at portionsindicated as “twice run portion” and “three-time run portion”, withupper side portions of run portions by two preceding heads. Thus, ineach comparatively great width run portion w1 indicated as “run portionW1 preceding to head gap”, the magnetic gap 13 can run on an old portionof the signal recording surface 21 a of the magnetic tape 21 on which apreceding head or heads have run (slidably moved).

[0023] From the foregoing, it can be recognized that the abrasionamounts at the tape sliding surface 12 and the magnetic gap 13 of thehead chip 11 by grinding force of very small magnetic particles and soforth sticking to the signal recording surface 21 a of the magnetic tape21 described hereinabove can be reduced with the head chip 11L which hasthe greater head contacting width W2 when compared with the head chip11S which has the smaller head contacting width W1.

[0024] However, if the head contacting width W2 of the tape slidingsurface 12 of the head chip 11 is merely increased as seen in FIG. 15B,then since the amount of air drawn in between the tape sliding surface12 and the magnetic tape 21 increases, the spacing or distance betweenthe head chip 11 and the magnetic tape 21 increases, resulting indecrease of the head output.

[0025] Therefore, it is demanded to decrease the abrasion of the headchip 11 by grinding force of very small magnetic particles and so forthwhile sufficient contact between the head and the tape is secured.

[0026] Therefore, in order to secure sufficient contact between the headand the tape, it has been conventionally proposed to form, as describedhereinabove with reference to FIGS. 14, 15A and 15B, a pair of upper andlower grooves 14 and 15 on the opposite upper and lower sides of themagnetic gap 13 in an upwardly and downwardly symmetrical relationshipon the tape sliding surface 12 such that they extend in parallel to thedirection of rotation of the head so that, upon helical scanning of themagnetic tape 21 by the head chip 11, the magnetic tape 21 may beattracted to the tape sliding surface 12 of the head chip 11 by anegative pressure effect by an air escaping action in the pair of upperand lower grooves 14 and 15, as disclosed in Japanese Patent LaidOpenNos. Hei 1-151019, Hei 1-235012, Hei 2-240806 and Hei 11-316904.

[0027] However, even if the countermeasure described is adopted, if thehead contacting width of the tape sliding surface 12 of the head chip 11is increased in an upwardly and downwardly symmetrical relationship asseen in FIG. 15B, then this likewise gives rise to a problem that thespacing between the head chip 11 and the magnetic tape 21 increases.Therefore, the countermeasure still has a limitation to increase of thehead contacting width while securing the head output.

[0028] On the other hand, in order to reduce the head abrasion, anothercountermeasure has been proposed wherein a plurality of dummy heads aredisposed at preceding positions to the plurality of rotating magneticheads 6 of the rotary head drum 1 such that the dummy heads grind verysmall magnetic particles and so forth sticking to the signal recordingsurface 21 a of the magnetic tape 21 earlier than the rotating magneticheads 6 while the rotating magnetic heads 6 helically scan the signalrecording surface 21 a of the magnetic tape 21.

[0029] Where the dummy heads are used in this manner, since the headgrinding force by very small magnetic particles and so forth on themagnetic tape 21 decreases in proportion to the number of times by whicha head runs on the magnetic tape 21 as seen from a graph of FIG. 18, thelife of the head can be increased.

[0030] However, where a plurality of dummy heads are mounted on therotary head drum 1 in this manner, this gives rise to another problemthat a rise in cost cannot be avoided, and besides, also the maintenancecost increases because it is necessary to replace the dummy heads whenthey are abraded.

[0031] Further, since a pair of grooves on a head chip are formed inparallel to the direction of rotation of the head chip, if foreignsubstances such as magnetic particles sticking to the surface of themagnetic tape are transferred and stick now between the pair of grooveson the tape sliding surface of the head chip on the leading side in thedirection of rotation of the head chip with respect to the magnetic gap,then the foreign substances such as the magnetic particles are carried,as the head chip rotates, in a direction parallel to the direction ofrotation of the head chip on the tape sliding surface until they come toand are accumulated in the magnetic gap thereby to frequently causeclogging of the magnetic gap.

[0032] Accordingly, only if a pair of grooves are formed on the oppositesides of the magnetic gap on the tape sliding surface of the head chipsuch that they extend in parallel to the direction of rotation of thehead chip, it is not easy to solve the problem of the spacing loss byclogging of the magnetic gap.

SUMMARY OF THE INVENTION

[0033] It is an object of the present invention to provide a magnetichead for a rotary head drum which can secure satisfactory contactingwith a magnetic tape and suppress abrasion thereof even if a dummy headis not disposed on the rotary head drum and besides can eliminate thespacing loss by clogging of the magnetic gap.

[0034] In order to attain the object described above, according to anaspect of the present invention, there is provided a magnetic head for arotary head drum, comprising a head chip having a tape sliding surfaceat an end thereof and having a magnetic gap formed on the tape slidingsurface, the tape sliding surface having a pair of grooves formed alongthe opposite sides of the magnetic gap in such a manner that the tapesliding surface is divided into three tape sliding surfaces including abelt-like central tape sliding surface on which the magnetic gap isformed and a belt-like upper side tape sliding surface and a belt-likelower side tape sliding surface formed on the opposite upper and lowersides of the central tape sliding surface with the pair of grooves lefttherebetween, a first one of the upper side tape sliding surface and thelower side tape sliding surface which is brought into contact with amagnetic tape earlier than the central tape sliding surface being formedwith an increased thickness, a second one of the upper side tape slidingsurface and the lower side tape sliding surface which is brought intocontact with the magnetic tape later than the central tape slidingsurface being formed with a decreased thickness.

[0035] With the magnetic head for a rotary head drum, from between theupper side tape sliding surface and the lower side tape sliding surfaceformed on the tape sliding surface at the end of the head chip on theopposite upper and lower sides of the central tape sliding surface,which has the magnetic gap thereon, with the pair of upper and lowergrooves left therebetween, the first tape sliding surface which isbrought into contact with a magnetic tape earlier than the central tapesliding surface is formed with an increased thickness while the secondtape sliding surface which is brought into contact with the magnetictape later than the central tape sliding surface is formed with adecreased thickness. Consequently, while sufficient contact between themagnetic tape and the central tape sliding surface which has themagnetic gap thereon is secured, very small magnetic particles and soforth sticking to the magnetic tape can be ground over a great width bythe first tape sliding surface which is brought into contact with themagnetic tape earlier than the central tape sliding surface of thepreceding head.

[0036] According to another aspect of the present invention, there isprovided a magnetic head for a rotary head drum, comprising a head chiphaving a tape sliding surface at an end thereof and having a magneticgap formed on the tape sliding surface, the tape sliding surface havinga pair of grooves formed along the opposite sides of the magnetic gap insuch a manner that the tape sliding surface is divided into three tapesliding surfaces including a belt-like central tape sliding surface onwhich the magnetic gap is formed and a belt-like upper side tape slidingsurface and a belt-like lower side tape sliding surface formed on theopposite upper and lower sides of the central tape sliding surface withthe pair of grooves left therebetween, the pair of grooves beinginclined with respect to a direction of rotation of the head chip.

[0037] With the magnetic head for a rotary head drum, the grooves formedalong the opposite sides of the magnetic gap on the tape sliding surfaceat the end of the head chip are inclined with respect to the rotationdirection of the head chip. Therefore, when the head chip is rotated torecord or reproduce a signal onto or from the magnetic tape, foreignsubstances such as magnetic particles transferred from the magnetic tapeto the tape sliding surface of the head chip on the leading side in therotation direction of the head chip are admitted from the tape slidingsurface into the grooves intermediately while they are carried towardthe magnetic gap side as the head chip rotates.

[0038] The above and other objects, features and advantages of thepresent invention will become apparent from the following descriptionand the appended claims, taken in conjunction with the accompanyingdrawings in which like parts or elements denoted by like referencesymbols.

BRIEF DESCRIPTION OF THE DRAWINGS

[0039]FIG. 1 is a schematic side elevational sectional view of a headchip of a rotating magnetic head for a rotary head drum to which thepresent invention is applied;

[0040]FIG. 2 is a perspective view of the head chip of FIG. 1;

[0041]FIG. 3 is a schematic view illustrating a running situation of thehead chip of FIG. 1 on a magnetic tape;

[0042]FIG. 4 is a schematic side elevational sectional view of a headchip of another rotating magnetic head for a rotary head drum to whichthe present invention is applied;

[0043]FIG. 5 is a schematic side elevational sectional view of a headchip of a further rotating magnetic head for a rotary head drum to whichthe present invention is applied;

[0044]FIG. 6 is a perspective view of a head chip of the magnetic headof FIG. 5;

[0045]FIG. 7 is a schematic side elevational sectional view of a headchip of a still further rotating magnetic head for a rotary head drum towhich the present invention is applied;

[0046]FIG. 8 is a perspective view of a head chip of the magnetic headof FIG. 7;

[0047]FIG. 9 is a sectional view taken along line A-A of FIG. 7;

[0048]FIG. 10 is an enlarged front elevational view illustratingadmission of a foreign substance such as a magnetic particle transferredto a tape sliding surface of the magnetic head of FIG. 7 into a grooveof the head chip;

[0049]FIG. 11 is a schematic side elevational sectional view of a headchip of a yet further rotating magnetic head for a rotary head drum towhich the present invention is applied;

[0050]FIG. 12 is a perspective view of an entire rotary head drum;

[0051]FIG. 13 is a bottom plan view of a rotary drum of the rotary headdrum of FIG. 12 and a perspective view of a head chip of the rotary headdrum;

[0052]FIG. 14 is a perspective view of a conventional head chip whichhas a small head contacting width;

[0053]FIGS. 15A and 15B are side elevational sectional viewsillustrating a difference of the spacing between a magnetic tape and amagnetic head between a head chip having a small head contacting widthand another head chip having an increased head contacting width;

[0054]FIG. 16 is a schematic view illustrating helical scanning of amagnetic tape by head chips;

[0055]FIGS. 17A and 17B are schematic views illustrating a difference ofthe running condition on a magnetic tape between a head chip having asmall head contacting width and another head chip having a great headcontacting width; and

[0056]FIG. 18 is a graph illustrating a decrease of the head grindingforce of a magnetic tape as the number of times by which a head runs onthe magnetic tape increases.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] Several magnetic heads for a rotary head drum to which thepresent invention are applied are described below with reference toFIGS. 1 to 11. It is to be noted that, in FIGS. 1 to 11, like elementsare denoted by like reference characters to those of FIGS. 12 to 18, andoverlapping description of them is omitted herein to avoid redundancy.

[0058] First, a rotating magnetic head for a rotary head drum to whichthe present invention is applied is described with reference to FIGS. 1to 3.

[0059] A head chip 11 of the rotating magnetic head 6 shown has a tapesliding surface 12 provided at a radially outer end thereof as describedhereinabove. The tape sliding surface 12 is divided into three tapesliding surfaces including a belt-shaped central tape sliding surface 12a and belt-shaped upper side tape sliding surface 12 b and lower sidetape sliding surface 12 c formed in parallel to the central tape slidingsurface 12 a on the opposite upper and lower sides of the central tapesliding surface 12 a with a pair of upper and lower grooves 14 and 15left therebetween, respectively. A magnetic gap 13 is formed at asubstantially center of the central tape sliding surface 12 a.

[0060] As described hereinabove with reference to FIG. 16, in a systemwherein the rotating magnetic head 6 helically scans a magnetic tape 21,which is fed at a constant speed in a direction indicated by an arrowmark a, in a direction indicated by an arrow mark b from a lower edge 21b side toward an upper edge 21 c side of the magnetic tape 21, the upperside tape sliding surface 12 b serves as a preceding tape contactingsurface which contacts with the magnetic tape 21 normally earlier thanthe central tape sliding surface 12 a in which the magnetic gap 13 isformed while the lower side tape sliding surface 12 c serves as a tapesliding surface which contacts with the magnetic tape 21 normally laterthan the central tape sliding surface 12 a. Incidentally, the upper sidetape sliding surface 12 b corresponds to a first tape sliding surfacedefined in the accompanying claims while the lower side tape slidingsurface 12 c corresponds to a second tape sliding surface defined in theaccompanying claims.

[0061] Thus, in the present first embodiment, where the thickness(vertical dimension in FIG. 1) of the central tape sliding surface 12 ais represented by T1 while the thickness of the upper side tape slidingsurface 12 b which contacts with the magnetic tape 21 earlier than thecentral tape sliding surface 12 a is represented by T2 and the thicknessof the lower side tape sliding surface 12 c which contacts with themagnetic tape 21 later than the central tape sliding surface 12 a isrepresented by T3, the tape sliding surface 12 is formed so as tosatisfy a relationship in thickness of T2>T1≧T3. It is to be noted that,where the thickness of the upper side groove 14 is represented by T4 andthe thickness of the lower side groove 15 is represented by T5, the tapesliding surface 12 is formed so as to satisfy a relationship inthickness of T4=T5.

[0062] It is to be noted that the dimensions may be, for example,T1=approximately 73 μm, T2=approximately 150 to 200 μm, T3=approximately54 μm, T4=approximately 150 μm and T5=approximately 150 μm.

[0063] With the head chip 11 of the rotating magnetic head 6 of thefirst embodiment having such a configuration as described above, whenthe “head 1”, “head 2”, “head 3” and “head 4” each including the headchip 11 having the tape sliding surface 12 successively helically scanthe signal recording surface 21 a of the magnetic tape 21, which is fedat a constant speed in the direction of the arrow mark a, in order at ahigh speed in the direction of the arrow mark b at a fixed track pitchP, an upper side portion of a run portion of the signal recordingsurface 21 a by a preceding head is overlapped twice as indicated by“twice run portion” and “three-time run portion” by a succeeding headand a next succeeding head.

[0064] In particular, similarly to the case wherein such a head chip 11Lhaving a head contacting width W2 increased uniformly on the upper andlower sides as described hereinabove with reference to FIGS. 15B and 17Bis employed, an upper side portion of a run portion (running locus) ofthe signal recording surface 21 a by a preceding head is run over(slidably moved) successively (repetitively by a plural number of times)by lower side portions of two succeeding heads.

[0065] Besides, as seen in FIG. 3, the magnetic gap 13 of a succeedinghead to a preceding head can run over an old portion of a comparativelygreat width of the signal recording surface 21 a of the magnetic tape 21as represented by “run portion W2 preceding to head gap” which has beenrun over (slidably moved) by the preceding head.

[0066] Accordingly, an effect (function) similar to that of a dummy headcan be provided to the upper side tape sliding surface 12 b having acomparatively great thickness T2 in that the head abrasion which isabrasion of the tape sliding surface 12 and the magnetic gap 13 of thehead chip 11 by grinding force of very small magnetic particles and soforth sticking to the signal recording surface 21 a of the magnetic tape21 can be suppressed and increase of the life of the head chip 11 can beanticipated.

[0067] Further, since the tape sliding surface 12 of the head chip 11 isformed such that the lower side tape sliding surface 12 c has adecreased thickness T3 while the upper side tape sliding surface 12 bhas an increased thickness T2 as seen in FIG. 1, the amount of air whichmay be admitted between the lower side tape sliding surface 12 c of thedecreased thickness T3 and the magnetic tape 21 can be reduced tosignificantly reduce the spacing between the lower side tape slidingsurface 12 c and the magnetic tape 21, and consequently, a sufficientlyhigh head output can be secured.

[0068] Referring now to FIG. 4, there is shown another magnetic head fora rotary head drum to which the present invention is applied.

[0069] In the present embodiment, the magnetic head is configured suchthat, in addition to the condition in thickness T2>T1≧T3, anothercondition in thickness of T4>T5 is satisfied and the thickness T4 is setto T4=approximately 160 to 200 μm.

[0070] Where the thickness T4 of the upper side groove 14 positionedjust below the upper side tape sliding surface 12 b having thecomparatively great thickness T2 is increased in this manner, airescaping through the upper side groove 14 increases its negativepressure effect of attracting the magnetic tape 21 to the upper sidetape sliding surface 12 b. Consequently, the spacing between the entiretape sliding surface 12 and the magnetic tape 21 can be further reduced,and a sufficiently high head output can be secured further readily.

[0071] Referring now to FIGS. 5 and 6, there is shown a further magnetichead for a rotary head drum to which the present invention is applied.

[0072] In the present third embodiment, the magnetic head according tothe first embodiment is modified such that a lower portion of the lowerside groove 15 is open at an open portion 16 thereof by cutting away thelower side tape sliding surface 12 c in such a manner that the tapesliding surface 12 is divided into two portions including the centraltape sliding surface 12 a and the upper side tape sliding surface 12 b.

[0073] Where the lower portion of the lower side groove 15 is open atthe open portion 16 in this manner, the spacing between the central tapesliding surface 12 a of the tape sliding surface 12, on which themagnetic gap 13 is provided, and the magnetic tape 21 can be furtherreduced. Consequently, a sufficiently high head output can be securedfurther readily.

[0074] Referring now to FIGS. 7 to 9, there is shown a still furthermagnetic head for a rotary head drum to which the present invention isapplied. A head chip 11 of the magnetic head according to the presentfourth embodiment is configured such that a pair of upper and lowergrooves 14 and 15 for allowing air to escape therethrough are formed inparallel to each other on the opposite upper and lower sides of amagnetic gap 13 formed at a substantially center of a tape slidingsurface 12 of the head chip 11 but in an inclined relationship by anangle of elevation of a predetermined inclination angle θ with respectto a rotatory direction A of the head chip 11.

[0075] Where the sliding width of the magnetic gap 13 on the magnetictape 21 is w while the length of the tape sliding surface 12 is L andthe length of the pair of grooves 14 and 15 is L, the grooves 14 and 15are preferably formed such that they satisfy

θ≧w/(L/2)  (1)

[0076] The inclination angle θ is preferably within 10° and mostpreferably approximately 4° to 6°.

[0077] With the head chip 11 of the rotating magnetic head 6 having sucha configuration as described above, when the magnetic gap 13 of the headchip 11 helically scans the signal recording surface 21 a of themagnetic tape 21 at a high speed along the rotatory direction A, such anair escaping action occurs that air between the tape sliding surface 12of the head chip 11 and the magnetic tape 21 escapes at a high speed inan obliquely downward direction b2 of an opposite direction B on thetrailing side of the rotatory direction A along and through the pair ofupper and lower grooves 14 and 15. Consequently, the magnetic tape 21 iscontacted with the tape sliding surface 12 of the head chip 11 (actuallyan air film on the submicron order is generated between the magnetictape 21 and the tape sliding surface 12) so that recording orreproduction of data onto or from the signal recording surface 21 a ofthe magnetic tape 21 is performed by the magnetic gap 13.

[0078] In this instance, if a foreign substance 31 such as a magneticparticle sticking to the signal recording surface 21 a of the magnetictape 21 is transferred to the tape sliding surface 12 of the head chip11 on the leading side in the rotatory direction A, then the foreignsubstance 31 such as a magnetic particle is carried in the oppositerotatory direction B by rotation of the head chip 11 and is likely to beaccumulated in the head chip 11.

[0079] However, since the pair of upper and lower grooves 14 and 15extending in parallel to each other on the opposite upper and lowersides of the magnetic gap 13 are inclined at an angle of elevation ofthe inclination angle θ with respect to the rotatory direction A as seenin FIGS. 7 to 9, a foreign substance 31 such as a magnetic particletransferred from the magnetic tape 21 to the tape sliding surface 12between the pair of upper and lower grooves 14 and 15 on the leadingside in the rotatory direction A of the magnetic gap 13 is admitted intothe upper side groove 14 intermediately while it is carried in theopposite rotatory direction B toward the magnetic gap 13 side on thetape sliding surface 12 as the head chip 11 rotates in the rotatorydirection A, as shown in FIG. 10. Consequently, the foreign substance 31such as a magnetic particle is prevented from arriving at and beingaccumulated in the magnetic gap 13.

[0080] Meanwhile, as shown in FIG. 10, a foreign substance 31 such as amagnetic particle transferred from the magnetic tape 21 to a position ofthe tape sliding surface 12 lower than the lower side groove 15 on theleading side of the magnetic gap 13 in the rotatory direction A isadmitted into the lower side groove 15 while it is carried in theopposite rotatory direction B on the tape sliding surface 12 as the headchip 11 rotates in the rotatory direction A. Consequently, also theforeign substance 31 can be prevented from arriving at and beingaccumulated in the magnetic gap 13.

[0081] Accordingly, with the head chip 11 having such a configuration asdescribed above, a foreign substance 31 such as a magnetic particletransferred from the magnetic tape 21 to the tape sliding surface 12 canbe prevented from arriving at and being accumulated in the magnetic gap13 and giving rise to the spacing loss, and consequently, recording orreproduction of a signal onto or from the magnetic tape 21 can beperformed normally with a high degree of accuracy (at a high density).

[0082] Further, it has been confirmed through an experiment that, wherethe inclination angle θ of the pair of upper and lower grooves 14 and 15with respect to the rotatory direction A is set to 4° to 6°, stabilityin feeding of the magnetic tape 21 in the opposite rotatory direction Bwith respect to the head chip 11 can be achieved while prevention of aforeign substance 31 such as a magnetic particle into the magnetic gap13 is achieved.

[0083] Further, where the pair of upper and lower grooves 14 and 15 areinclined at an angle of elevation with respect to the rotatory directionA in this manner, when air escapes at a high speed in the obliquelydownward direction b2 of the opposite rotatory direction B within andthrough the upper and lower grooves 14 and 15, pushing down force in adownward direction b1 acts upon the magnetic tape 21 and tends to pressthe lower edge 21 b of the magnetic tape 21 against the helical tapelead 8 of the fixed drum 2 of the rotary head drum 1 as seen in FIGS. 7and 12. Consequently, also an advantage that the magnetic tape 21 can behelically fed stably can be anticipated.

[0084] Referring now to FIG. 11, there is shown a yet further rotatingmagnetic head for a rotary head drum to which the present invention isapplied. A head chip 11 of the rotating magnetic head according to thepresent fifth embodiment is generally configured such that a pair ofupper and lower parallel grooves 14 and 15 are inclined at a depressionangle of a predetermined angle θ with respect to a rotatory direction Aof the head chip 11.

[0085] With the head chip 11 shown in FIG. 11, a foreign substance 31such as a magnetic particle transferred from the magnetic tape 21 to thetape sliding surface 12 between the pair of upper and lower grooves 14and 15 on the leading side in the rotatory direction A of the magneticgap 13 is admitted into the lower side groove 15 intermediately while itis carried in the opposite rotatory direction B toward the magnetic gap13 side on the tape sliding surface 12 as the head chip 11 rotates inthe rotatory direction A. Consequently, the foreign substance 31 such asa magnetic particle can be prevented from arriving at and beingaccumulated in the magnetic gap 13.

[0086] Meanwhile, a foreign substance 31 such as a magnetic particletransferred from the magnetic tape 21 to a position of the tape slidingsurface 12 higher than the upper side groove 14 on the leading side ofthe magnetic gap 13 in the rotatory direction A is admitted into theupper side groove 14 while it is carried in the opposite rotatorydirection B on the tape sliding surface 12 as the head chip 11 rotatesin the rotatory direction A. Consequently, also the foreign substance 31can be prevented from arriving at and being accumulated in the magneticgap 13.

[0087] It is to be noted that, as shown in FIG. 10, the opposite upperand lower faces 11 a and 11 b at the tip end of the head chip 11connected to the tape sliding surface 12 may be formed in parallel tothe rotatory direction A of the head chip 11 as indicated by solid linesin FIG. 11 or may otherwise be formed in parallel to the upper and lowergrooves 14 and 15 inclined by the inclination angle θ with respect tothe rotatory direction A of the head chip 11 as indicated by brokenlines in FIG. 10.

[0088] While several embodiments of the present invention have beendescribed above, the present invention is not limited to the embodimentsdescribed above but allows various modifications based on the technicalscope thereof.

[0089] For example, in the embodiments described above, since the headchip 11 helically scans the magnetic tape 21 in an obliquely upwarddirection from the lower edge 21 b toward the upper edge 21 c of themagnetic tape 21, that one of the upper side tape sliding surface 12 band the lower side tape sliding surface 12 c which is brought intocontact with the magnetic tape 21 earlier than the central tape slidingsurface 12 a is the upper side tape sliding surface 12 b. However, inanother system wherein the head chip 11 helically scans the magnetictape 21 in an obliquely downward direction from the upper edge 21 ctoward the lower edge 21 b of the magnetic tape 21, that one of theupper side tape sliding surface 12 b and the lower side tape slidingsurface 12 c which is brought into contact with the magnetic tape 21earlier than the central tape sliding surface 21 a is the lower sidetape sliding surface 12 c.

[0090] Accordingly, the rotating magnetic head 6 of the presentinvention may have a structure inverted from any of those shown in FIGS.1 to 6.

What ts claimed is:
 1. A magnetic head for a rotary head drum,comprising: a head chip having a tape sliding surface at an end thereofand having a magnetic gap formed on said tape sliding surface, said tapesliding surface having a pair of grooves formed along the opposite sidesof said magnetic gap in such a manner that said tape sliding surface isdivided into three tape sliding surfaces including a belt-like centraltape sliding surface on which said magnetic gap is formed and abelt-like upper side tape sliding surface and a belt-like lower sidetape sliding surface formed on the opposite upper and lower sides ofsaid central tape sliding surface with said pair of grooves lefttherebetween, a first one of said upper side tape sliding surface andsaid lower side tape sliding surface which is brought into contact witha magnetic tape earlier than said central tape sliding surface beingformed with an increased thickness, a second one of said upper side tapesliding surface and said lower side tape sliding surface which isbrought into contact with the magnetic tape later than said central tapesliding surface being formed with a decreased thickness.
 2. A magnetichead for a rotary head drum, comprising: a head chip having a tapesliding surface at an end thereof and having a magnetic gap formed onsaid tape sliding surface, said tape sliding surface having a pair ofgrooves formed along the opposite sides of said magnetic gap in such amanner that said tape sliding surface is divided into three tape slidingsurfaces including a belt-like central tape sliding surface on whichsaid magnetic gap is formed and a belt-like upper side tape slidingsurface and a belt-like lower side tape sliding surface formed on theopposite upper and lower sides of said central tape sliding surface withsaid pair of grooves left therebetween, a first one of said upper sidetape sliding surface and said lower side tape sliding surface which isbrought into contact with a magnetic tape earlier than said central tapesliding surface being formed with an increased thickness, a second oneof said upper side tape sliding surface and said lower side tape slidingsurface which is brought into contact with the magnetic tape earlierthan said central tape sliding surface being formed with a decreasedthickness, that one of said grooves which is positioned between saidcentral tape sliding surface and the first tape sliding surface beingformed with a thickness greater than that of the other groove which ispositioned between said central tape sliding surface and the second tapesliding surface.
 3. A magnetic head for a rotary head drum, comprising:a head chip having a tape sliding surface at an end thereof and having amagnetic gap formed on said tape sliding surface, said tape slidingsurface having a groove formed along an upper side or a lower side ofsaid magnetic gap in such a manner that said tape sliding surface isdivided into two tape sliding surfaces including a belt-like centraltape sliding surface on which said magnetic gap is formed and abelt-like upper side tape sliding surface or a belt-like lower side tapesliding surface formed on the upper side or the lower side of saidcentral tape sliding surface with said groove left therebetween, saidupper side tape sliding surface or said lower side tape sliding surfacewhich is brought into contact with a magnetic tape earlier than saidcentral tape sliding surface being formed with a thickness greater thanthat of said central tape sliding surface, a portion of said head chipon the opposite side to said upper side tape sliding surface or saidlower side tape sliding surface with respect to said central tapesliding surface being open at an open portion parallel to said groove.4. A magnetic head for a rotary head drum, comprising: a head chiphaving a tape sliding surface at an end thereof and having a magneticgap formed on said tape sliding surface, said tape sliding surfacehaving a pair of grooves formed along the opposite sides of saidmagnetic gap in such a manner that said tape sliding surface is dividedinto three tape sliding surfaces including a belt-like central tapesliding surface on which said magnetic gap is formed and a belt-likeupper side tape sliding surface and a belt-like lower side tape slidingsurface formed on the opposite upper and lower sides of said centraltape sliding surface with said pair of grooves left therebetween, saidpair of grooves being inclined with respect to a direction of rotationof said head chip.
 5. A magnetic head for a rotary head drum accordingto claim 4, wherein said grooves are formed so as to satisfy θ≧w/(L/2)where w is the sliding width of said magnetic gap with respect to themagnetic tape, L is the length of said tape sliding surface over whichsaid tape sliding surface contacts with the magnetic tape and θ is theinclination angle of said grooves.